1. Field of Invention
The present disclosure relates to a grid-connected inverter. More particularly, the present disclosure relates to a starter of a grid-connected inverter and a control method thereof.
2. Description of Related Art
With the ever-increasing seriousness of energy-related problems in recent times, the development of new ways in which to generate energy (e.g., wind energy, solar energy, etc.) is attracting the attention of those involved in research and development in various fields. In a power generation system, the frequency and phase of the AC (alternating current) voltage outputted by the power generator are often different from those of the AC electric grid. Thus, the AC voltage outputted by the power generator is generally converted into a DC (direct current) voltage through an inverter (or a converter), and subsequently the DC voltage is inverted to another AC voltage having the same frequency and phase as the AC electric grid, so as to realize grid-connected power generation. In the process of converting the AC voltage into the DC voltage and subsequently inverting the DC voltage into another AC voltage, electronic components (e.g., power switching valves) are PWM (pulse-width modulation)-controlled, and the AC-DC conversion and DC-AC conversion are realized by turning on or off these power switching valves.
Furthermore, as such electronic components are widely applied, the problem of harmonic waves and asymmetry of the power system is becoming more and more serious, and this is greatly harmful to the operation safety, stability and reliability of the grid-connected inverter mentioned above. As a result, it becomes necessary to suppress the harmonic waves and perform harmonic compensation. One solution of the prior art involves using an active power filter (APF) to realize harmonic compensation. However, in such an APF, the inductance at the AC side is often small, and only a filter capacitor is arranged at the DC side. Thus if the APF is incorporated into an AC electric grid without a soft start process, a large start-up inrush current will be generated, which greatly threatens the safety of the power components, and may even cause failure of the APF grid connection.
In view of this, many in the industry are endeavoring to find ways in which to design a starter of a grid-connected inverter and reasonably control the starter, so as to minimize the inrush current during start-up of the grid-connected inverter while avoiding increases in the capacity and cost of the system, and also so as to protect the power switch components and incorporate the inverter into the electric grid through a soft start process.